In the latest edition of the official Spider-Man handbook, there's an entry for American Son a.k.a. Gabriel Stacy. While explaining his origins, the entry mentions that Gwen's one night stand with Norman occured shortly after he saved her from the Kingpin. I remember that MadGoblin suggested the same idea in one of his Goblin articles years ago, so I thought it was cool that it's now the official explanation for what happened. Maybe someone at Marvel's been looking at his site!

Personally, I'm glad they used that idea since I think it fits better with the characters. Gwen was single at the time, so it's not like she was cheating on Peter or Harry, and her actions make a lot more sense when you consider that Norman had just saved her and her father's lives. It also means that Norman was still "good" Norman at the time, so it's not like he was doing it just to spite Peter or anything like that. Once he was back to being his usual bastard self, he might've even seen his affair with Gwen as a moment of weakness to be ashamed of. It'd explain why he didn't mention it again for so long...